A Rankine cycle system in which engine waste heat is reused as energy is known. The engine waste heat is recovered, the Rankine cycle is operated with the waste heat, and rotational energy is produced by an expander (turbine). As an example of such system, a waste heat recovery apparatus has been disclosed (JP 2010-101283 A). The waste heat recovery apparatus is provided with a turbine that is driven by steam with which engine waste heat is recovered in a superheater, and with a power recovery means. The power recovery means includes a first pulley connected to the shaft of the turbine via an electromagnetic clutch, and a second pulley disposed on the crank shaft. The power recovery means recovers power from the turbine to the crank shaft via a belt extended across the first pulley and the second pulley. The waste heat recovery apparatus is also provided with an ECU that, when it is determined that the rotation of the turbine is excessive, adjusts the load on the shaft of the turbine by connecting the first pulley to the shaft of the turbine via the electromagnetic clutch.